Simplify the expression. $(-3r^{4}-6r)(-4r^{3}-r^{2})$
Solution: First use the distributive property. $ - 3 r^4 (-4 r^3) - 3 r^4 (- r^2) - 6 r (-4 r^3) - 6 r (- r^2) $ Simplify. $12r^{7}+3r^{6}+24r^{4}+6r^{3}$